基于双变量控制原理的变压变频新方法

阐述了在变频调速系统中运用变压变频技术的必要性,分析了使用传统余弦交点法进行在线变压变频存在的缺陷,进而提出了基于双变量控制原理、自然无环流控制和对称余弦法的变压变频新方法,给出了在保持输出频率不变条件下闭环调压的具体实现方法。对变压变频新方法的实验结果进行了仿真、分析和比较,验证了新方法具有良好的控制效果。     

基于SIMULINK的变频器仿真研究

为了掌握交流变频技术及其应用,针对交交（ACAC）变频和交直交（ACDCAC）变频器技术,从这两种变频电路原理出发,采用SIMULINK工具箱对一种ACAC和一种ACDCAC变频电路进行研究,采用模拟仿真方法对变频调速系统进行分析,设计了ACAC和ACDCAC变频器的SIMULINK模型并进行仿真。通过分析仿真结果展现了交交变频和交直交变频具有的相同和不同点。这种仿真分析方法是学习和理解交流变频技术更有效途径,也是验证变频系统可行性的有效措施。     

“跳相”思想在三重化交交变频电路中的运用

"跳相"交交变频是在传统交交变频基础上的扩展,可以将输出频率提高到接近工频频率,且具有无环流、无死区的优点。与单重化交交变频相比,三重化"跳相"交交变频电路具有改变输出电压的能力,相对于现有变频器具有容量大、电压等级高、成本低的优点。以反并联桥电路为基础介绍了"跳相"交交变频的基本思想,以三重化为例,根据电压矢量叠加的方法分析了可能的叠加结果,总结出电压变化的范围,并从中选出三组作为实例,用MATLAB进行了仿真,最后搭建了实验平台,进行了实验分析。实验结果表明理论和仿真分析正确。     

三重化“跳相”交交变频电路的研究

“跳相”交交变频是在传统交交变频的基础上的扩展,可以将输出频率提高到接近工频频率,且具有无环流、无死区的优点。与单重化交交变频相比,三重化“跳相”交交变频电路具有改变输出电压的能力,相对于现有变频器具有容量大、电压等级高、成本低的优点。以反并联桥电路为基础介绍了“跳相”交交变频的基本思想,以三重化为例,根据电压矢量叠加的方法分析了可能的叠加结果,总结出电压变化的范围,并从中选出三组作为实例,用MATLAB进行了仿真,最后搭建了实验平台,进行了实验分析,实验结果表明理论和仿真分析正确。     

移相变频原理之研究

本文首次提出一种用于移相变频器的新的理论分析方法,即传统的相控式交交变频器所采用的波形交叉原理。分析结果表明,移相变频器实际上是相控式交交变频器的一个特例,借助于波形交叉原理可以完整地描述移相变频器的各种工作状态。本文还讨论了移相变频器的一些性能参数,并提供了计算方法,可供此类变频系统设计时参考。     

交—交变频器的环流与环流电抗器

针对行环流交交变频装置的环流电抗器国内国外资料都很缺乏的情况,本文从有环流交交变频装置的优缺点出发,提出了对环流电抗器的要求,进而阐述了环流电抗器的类型,性能特点,结构特点,非线性环流电抗器的计算原理和计算方法,并阐明了利用错位的方法进行选组的原理、影响环流的因素及选组的效果。     

移相变频原理之研究

本文首次提出一种用于移相变频器的新的理论分析方法,即传统的相控式交交变频器所采用的波形交叉法。分析结果表明,移相变频器实际上是相控式交交变频器的一个特例,借助于波形交叉原理可以完整地描述移相变频器的各种工作状态。在上述基础上,本文讨论了移相变频器的一些性能参数,诸如变频范围、转换特性、功率因数、输出电压及其波形参数等,并提供了计算方法,可供此类变频系统设计时参考。     

磁场定向控制交交变频同步电机系统的数学模型

在同步电机、交交变频器和磁场定向控制系统方程的基础上，提出了磁场定向控制交交变频同步电机系统完整的数学模型。编制了相应的数字模拟程序，采用四阶龙格一库塔法解同步电机的状态方程，而离散相似法用于控制系统方程的求解。在实验室建立了由一台４０ｋＷ三相凸极同步电机、交交变频器和磁场定向控制系统组成的小容量试验系统。进行了两种情况的动态实验，并与相应的仿真结果进行了对比。比较结果表明了上述数学模型的正确性。     

脉冲阻塞式交交变频系统的动态性能研究

为了提高交交变频系统的稳定性,改善其动态性能,进行了基于脉冲阻塞斩波控制的动态性能分析.文中介绍了脉冲阻塞式交交变频系统的结构和变频原理,建立了其主要模块的数学模型,应用MATLAB环境进行了模型搭建,分析了系统中结构参数对其动态性能影响的变化规律,为脉冲阻塞式交交变频系统的性能优化设计提供了依据.     

基于矩阵式交交变频的柔性分频输电系统仿真

提出了采用矩阵式交交变频器作为倍频设备的柔性分频输电系统，在MATLAB／Simulink环境下搭建了仿真模型，研究系统的传输容量和效率、谐波和无功等问题，并和其它的输电方式进行了比较。分析结果表明，基于矩阵式交交变频的柔性分频输电系统在开发利用我国的水电资源和远距离输电中是一种极有潜力的输电方式。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that